This invention relates to a testing device for a pilot valve controlling a main valve in a main flow line, and more particularly to such a testing device and testing method for a so called non-flowing pilot valve which is non-flowing during normal operation.
A non-flowing pilot valve does not permit direct fluid communication between its inlet and outlet fluid chambers as an intermediate fluid chamber is provided between the inlet and outlet fluid chambers and a valve member in the intermediate chamber prevents direct fluid communication between the inlet and outlet chambers. The inlet chamber is normally a fluid sensing chamber having a sensing diaphragm therein. The main valve, which may be a pressure relief or throttling control valve, normally has a so called dome with a pressure responsive member therein, such as a diaphragm or piston, which is responsive to fluid pressure from the intermediate chamber of the pilot valve. The intermediate fluid chamber is never in simultaneous fluid communication with both the inlet and outlet fluid chambers. Thus, in a non-flowing pilot valve, there is no continuous fluid flow through the pilot valve from a bypass line extending from the main flow line as the inlet and outlet lines to the pilot valve are never in simultaneous fluid communication with the intermediate chamber.
The elimination of a continous fluid flow through the pilot valve removes many of the problems in pilot valves having a continuous fluid flow such as, for example, the clogging of orifices and the like with entrained foreign matter in the flowing fluid, or icing resulting from wet gas applications. While a relatively small amount of fluid may be transmitted through the pilot valve during operation, this amount is insignificant.
Such a non-flowing pilot valve is highly sensitive or responsive to changes in the sensed fluid pressure. The responsiveness of the non-flowing pilot valve to pressure changes in a sensed fluid is relatively constant over its operating range and a non-flowing pilot valve has a fast response to pressure changes in the sensed fluid.
It is desirable to have field testing of such a non flowing pilot valve periodically to insure that the pilot valve is operating properly and without such testing affecting the normal operation of the main valve. For such a testing operation or procedure when the main valve is a pressure relief valve, it is necessary to inject test pressure from an auxiliary fluid pressure source into the sensing chamber of the pilot valve in order to simulate an increase in fluid pressure from a main flow line or fluid tank, for example. The fluid inlet sensing chamber for a pilot valve normally has a sensing diaphragm therein and if test pressure is applied to the sensing chamber above the fluid pressure set point for the main pressure relief valve, an over pressurizing of the diaphragm chamber could occur which might damage the pilot valve. Also, if the fluid pressure in the inlet sensing chamber rises above the set fluid pressure for the main pressure relief valve this would normally result in a proportional decrease of dome fluid pressure to the main valve thereby allowing opening of the pressure relief valve which is not desirable for a testing operation.